JP 2007-253714 A discloses an in-vehicle radar equipment for determining whether or not a preceding vehicle exists on an own lane on which a subject vehicle travels by using a virtual determination width for own lane. When the radar equipment recognizes a nearest preceding vehicle to the subject vehicle among the surrounding vehicles of the subject vehicles which are detected by an in-vehicle radar within a determination width for own lane, it recognized the nearest preceding vehicle as the preceding vehicle on the own lane. Once the radar equipment recognized the nearest preceding vehicle on the own lane, it applies a wide determination width for own lane to the nearest preceding vehicle on the own lane while applying a narrow determination width for own lane to the other preceding vehicles.
According to the radar equipment, once the nearest preceding vehicle on the own lane is recognized, it is possible to prevent other vehicles on the adjacent lane from being erroneously recognized as the preceding vehicle on the own lane. However, before recognizing the nearest preceding vehicles on the own lane, the following problem arises. That is, when the nearest preceding vehicle on the own lane has not been recognized whereas a nearest preceding vehicle to the subject vehicle which is detected by the in-vehicle radar travels far from the subject vehicle, it is difficult to distinguish whether or not the detected nearest preceding vehicle travels on the own lane or the adjacent lane.
If a default value of the determination width for own lane is set to a narrow width, it is possible to prevent the detected nearest preceding vehicle from recognizing as the nearest preceding vehicle on the own lane even though it actually travels on the adjacent lane. However, when the default value is set to the narrow width, it takes time to recognize a true object to be recognized on the own lane. This is because if the default value is set to the narrow width, it is not able to recognize the true object until the distance to the subject vehicle decreases to some extent.
If it takes time to recognize the true object to be recognized, the following problem occurs when the subject vehicle traveling at high speed catches up with a tail of a traffic congestion. That is, when a preceding vehicle of the subject vehicle is located in the tail of the traffic congestion, in order to prevent collision with this rearmost vehicle, it is necessary for the subject vehicle to start decelerating assist control from a relatively long distance. However, when it takes time to recognize the rearmost vehicle, the decelerating assist control will be started after the subject vehicle approaches the rearmost vehicle to some extent. Therefore, it is necessary for the subject vehicle to start rapid deceleration, which gives a sense of discomfort to occupant of the subject vehicle.
The present disclosure addresses the above described problem, and an object of the present disclosure is, to provide measures to prevent the subject vehicle from colliding with a nearest preceding vehicle even in a case where it is difficult to distinguish the lane along which the nearest preceding vehicle travels.